Waterflood stabilization for paraffinic crude oils

ABSTRACT

Disclosed herein is a waterflooding process wherein paraffinic precipitation is avoided in reservoirs containing paraffinic crude oils, having ambient reservoir temperatures near the pour point of the crude oil. The process of the present invention involves the introduction of thermal energy into the waterflood media in order to raise the temperature of the injected water to about 10* to about 20*F. higher than the pour point or ambient temperature of the reservoir. Through this energy addition, the water injection and subsequent drive of crude oil through the reservoir does not significantly lower the temperature of the paraffinic crude so as to avoid precipitation of paraffin within the reservoir and provide an efficient waterflooding procedure.

United States Patent Harry 1 Nov. 28, 1972 [54] WATERFLOOD STABILIZATION F0 PARAFFINIC CRUDE OILS [72] Inventor: Robert Y. Harry, Midland, Tex.

[73] Assignee: Cities Service Oil Company [22] Filed: June 18, 1971 [21] Appl. No.: 154,618

[52 as. C] ..l66/272 51] 1111. C1. ..E2lb 43/24 [58] Field 61 Search ..166/272, 303

561' References Cited UNITED STATES PATENTS 1,263,618 4/1918 Squires ..l66/272 X 3,204,694 9/1965 Johnson ..166/272 x 3,333,632 8/1967 Kyte ..166/272 3,385,359 5/1968 Offeringa 166/272 x 3,572,437 3/1971 Marberry 166/272 Primary Examiner-Robert L. Wolfe Attorney-J. Richard Geaman '[57 v ABsmAcr Disclosed herein is a waterflooding process wherein paraflinic precipitation is avoided in reservoirs containing paraffinic crude oils, having ambient reservoir temperatures near the pour point of the crude oil. The process of the present invention involves the introduction of thermal energy into the waterflood media in order to raise the temperature of the injected water to about 10 to about 20F. higher than the pour point or ambient temperature of the reservoir. Through this energy addition, the water injection and subsequent drive of crude oil through the reservoir does not significantly lower the temperature of the' parafiinic crude so as to avoid precipitation of paraffin within the reservoir and provide an efficient waterflooding procedure.

6 Chins, No Ih'awings BACKGROUND OF THE INVENTION The present invention relates to a process for the waterflooding and stabilization of paraffinic crude oils. More particularly, the present invention involves thermal energy addition into a waterflooding media to raise the temperature of the injected waterflood media to slightly above the ambient temperature of the paraffinic crudes contained within a reservoir in order to stabilize the paraffinic crude during production.

Various and sundry reservoirs exist which have a low ambient reservoir temperature. By low temperature is meant reservoir temperatures below approximately 100F. Many of these low temperature reservoirs conjunctively have a reservoir crude containing a large concentration of paraffinic hydrocarbons. These reservoirs produce an unstable physical balance in that any transient reservoir conditions, for example a Slight lowering of pressure, will bring the reservoir crude to within its pour point conditions. As the pour point is neared, the paraffins contained within the crude oil begin to precipitate in the vicinity of the wellbore, thereby blocking the wellbore and preventing further crude oil production.

Numerous techniques have been applied in the prior art for control of paraffin wellbore blockage so as to improve paraffinic crude oil production. Typical of these methods are the introduction of a downhole heater into a production wellbore in order to raise the solubility of the paraffinic crude about the wellbore by raising the temperature of the crude oil and its ability to contain the paraffinic crude oil in solution. Particular problems are incurred when paraffinic crude oil containing reservoirs, having low ambient temperatures are waterflooded. Generally, during waterflooding, the water introduced into the reservoir has a temperature below that of the ambient temperature of the reservoir. Paraffinic crude oils exhibit a delicate balance between the solubility of the paraffin in the crudeoil and the precipitation of the crude oil onto the interstices of the reservoir. A slight decrease in temperature about a water injection well may inhibit further secondary oil recovery through precipitation of paraffin as the crude oil comes in contact with the lower temperature water. Often, unprecipitated paraffins are carried within the crude oil in a very name r65; until'tlieEi-iid'ebil reaches a production well, at which point the paraffins are precipitated. The introduction of a downhole heater is representative of the preventative apparatus utilized in production wells. Downhole heaters, generally, are ineffective as the parafiinic precipitate is near irreversible and is difi'icult to remove even through the backwashing of heated solvents into a production well or by other expensive and complicated procedures.

What is required is a method for producing parafiinic crude oils by secondary recovery through waterflooding in reservoirs having low ambient reservoir temperatures and therefore being near the pour point of the crude oil.

It is an object of the present invention to provide a method for waterflooding paraffinic crude oil containing reservoirs in order to provide a stabilized production process.

It is a further object of the present invention to provide a waterflooding process wherein parafl'mic crude oils may be produced without paraffin precipitate being fonned during the waterflooding operation.

It is still a further object of the present invention to provide a process for waterflooding of paraffinic crude oils wherein the water-flooding media has thermal energy introduced therein in order to raise the temperature of the waterflooding media to about 10F. to about 20F. higher than the pour point temperature of the reservoir fluid in order to stabilize the waterflooding of the'parafi'mic crude oil containing reservoir.

With these and other objects in mind, the present invention may be more fully understood through the following discussion and description:

SUMMARY OF THE INVENTION The objects of the present invention are accomplished through a secondary oil recovery process for the waterflooding of oil reservoirs containing a high concentration of parafiinic hydrocarbons with a waterflooding media normally having a temperature lower than that of the ambient reservoirtemtiiaifiam pour point of the paraffinic crude. The improvement in the secondary oil recovery process comprises raising the temperature of the introduced waterflooding media to about 10F. to about 20F. above the pour point temperature of the reservoir fluidto form a heated waterflooding media. The process prevents a shocking of the reservoir crude oil during the introduction of the waterflooding media and thereby stabilizes the waterflooding process and prevents paraffinic precipitate from forming in the reservoir and blocking the production wellbore.

" DETAILED DESCRIPTION OF THE INVENTION As disclosed, the process of the present invention is a method for preventing paraffinic precipitation in those reservoirs containing paraffinic crude oils or those crudes having a high paraffinic hydrocarbon concentration. The process is particularly applicable within reservoirs having a low ambient reservoir temperature during waterflooding for the secondary oil recovery of the paraffinic crudes. A particular aspect of the present invention involves the addition of thermal energy to the water injected into the reservoir by raising the temperature of the injected water to about 10F. to about 20F. higher than the ambient temperature of the reservoir or the pour point of the crude oil contained therein. Through this energy addition, the water injection and subsequent driving of the crude oil through the reservoir does not shock the crude oil or lower its temperature significantly, thereby preventing the paraffinic hydrocarbons from being precipitated in the interstices of the reservoir rock matrix. The injection of a slightly heated waterflooding media yields more favorable mobility ratios as derived by the contacting of a fluid slightly above the reservoir temperature with the paraffinic crude oil. This phenomenon is primarily due to the paraffinic crude oil exhibiting a mobility ratio with a cooler waterflooding media of from about 3 to about 50, whereas with the process of the present invention, due to the non-precipitation of the paraffin in part or total within the crude oil, the mobility ratio remains approximately unity and thereby favorable for the wateris further aided through the introduction of heat into the production wellbore during the waterflooding media introduction. The addition of a wellbore heater prevents paraffinic precipitation in the production well-bore andallows for uncomplicated removal of the paraffmic crude at the production wellhead. The heating of the production wellbore may be accomplished by any of the various and sundry downhole wellbore heating devices, for example electric heaters or chemical reaction exothermic heat being supplied to the wellbore.

in a further preferred embodiment of the present invention, the improved secondary oil recovery process may further comprise lowering the temperature of the introduced waterflooding medium to its original temperature by lowering the amount of thermal energy supplied to the waterflooding media in order to return the waterflooding media to its original temperature. This lowering of the temperature of the introduced waterflooding media is brought to occur after at least 0.5 pore volumes of heated waterflooding medium have beenintroduced into the reservoir. The further introduction of the cooled waterflooding media allows paraffinic precipitation about the injection well in order to provide a selective plugging of the more permeable strata contained with the reservoir such that a more efficient waterflood is conducted in that the water is forced to sweep the less permeable zones of the reservoir and thereby provide a more efficient oil recovery process. As in conjunction with the preferred embodiment of the present invention, the production wellbores may be heated during the waterflooding media introduction in order to provide a more readily removable produced fluid forincreased ease of the oil production from the reservoir and to prevent paraffinic precipitation therein the production wells.

It is still a further embodiment of the present invention that the improved secondary oil recovery process further comprise reintroducing the heated waterflooding media having a temperature to F. above the pour point temperature of the reservoir fluid after 0.1 to about 0.3 pore volumes of unheated waterflooding media have been introduced into the reservoir. Through this procedure the previously selectively plugged more permeable strata remain blocked, while heated waterflooding media is simultaneously introduced into the less permeable zones of the formation allowing for greater horizontal and vertical sweep therein the reservoir and for greater recovery of oil therefrom. As in the other preferred embodiments of the present invention, the production wellbore is also preferably heated during the waterflooding medium introduction to provide the more efficient oil production therefrom.

As an example of the applicability of the present invention, the following waterflooding process may be utilized:

EXAMPLE In the waterflooding of various paraffinic hydrocarbon containing crude oils, the exact amount of waterflooding media heating required for the relative amounts of parafiinic hydrocarbons contained with the crude oils may be approximated through the utilization of' the accompanying Table. In the Table, the degrees of temperature rise require for the waterflooding media having the particular temperature before thermal energy introduction is shown for various concentrations of paraffinic hydrocarbons within the crude oil with a pour point of the crude oil depicted for those'parafflnic concentrations. Therefore, as an example, if the ambient reservoir temperature of a reservoir is 90F. with a pour point of the paraffinic crude contained therein being 80F. a waterflooding media having an initial temperature of 80F. requires thermal energy introduction in order to raise the overall temperature of the waterflooding medium 20F. in order to form a stabilized waterflooding media for the secondary oil recovery project.

TABLE waterflooding ambient waterflooding pour point media reservoir media of paraflinic temperature rise temperature temperature F crude oil required 50F 60F 25F F 60F 70F 25F F 70F 70F 20F F 80F 80F 20F l00F 90F 80F 20F 1 l0F F 80F Therefore, through the utilization of the process of the present invention, stabilizationand consistency of reservoir fluid is obtained such that a more desirable secondary oil recovery process may be provided for those reservoirs having high paraffmic hydrocarbon content and exhibiting an ambient reservoir temperature near that of the pour point of the crude oil contained therein. The process obviates any paraffinic precipitation within the reservoir or about the production wellbore, thereby preventing blockage of crude oil production from the crude oil reservoir and enhances the oil recovery therefrom.

While the invention has been described above with respect to certain embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth herein.

Therefore, I claim:

1. An improved secondary oil recovery process for the waterflooding of oil reservoirs containing a high concentration of paraffinic hydrocarbons with a waterflooding media normally having a temperature lower than that of the reservoir wherein the reservoir exhibits an ambient reservoir temperature near the pour point of the paraffinic crude, the improvement comprising raising the temperature of the introduced waterflooding media to about 10F. to about 20F. above the pour point temperature of the reservoir fluids to form a heated waterflooding media.

bore during the waterflooding media introduction.

5. The improved secondary oil recovery process of claim 3 further comprising reintroducing the heated waterflooding media after about 0.1 to about 0.3 pore volumes of unheated waterflooding media have been introduced.

6. The improved secondary oil recovery process of claim 5 further comprising heating the production wellbores during the water-flooding media introduction. 

2. The improved secondary oil recovery process of claim 1 further comprising heating the production wellbores during the waterflooding media introduction.
 3. The improved secondary oil recovery process of claim 1 further comprising lowering the temperature of the introduced waterflooding media to its original temperature after at least 0.5 pore volumes of heated waterflooding media have been introduced.
 4. The improved secondary oil recovery process of claim 3 further comprising heating the production wellbore during the waterflooding media introduction.
 5. The improved secondary oil recovery process of claim 3 further comprising reintroducing the heated waterflooding media after about 0.1 to about 0.3 pore volumes of unheated waterflooding media have been introduced.
 6. The improved secondary oil recovery process of claim 5 further comprising heating the production wellbores during the water-flooding media introduction. 